I've enjoyed working with recycled sari silk ribbon yarn lately. After checking out how the sari strips are sewn together, I figured out how to make silk ribbon yarn using thrifted silk garments.
I made a 90 gram skein-36 yards-with 2 voluminous shirts (pretty sure I had that exact pink shirt from Express in 1993...) and 1 knee length skirt.
Cut garments apart at seams into pieces-cut off seams, cuffs, collars, button bands waist bands-anything that will keep the fabric from ripping cleanly. Keep an eye out-both of the shirts I used had real shell buttons for my button jar... Once you have pieces of fabric free of all that, make cuts 1-1 1/2 inches apart on a narrow side making sure the cuts are parallel to the grain of the fabric. Use the cuts you made as the starting points to rip the fabric into strips. You may have to pull off the worst of the loose threads, but don't obsess about trimming them all-they add texture.
Have the strips of silk in a pile next to your sewing machine. Grab two and stack them one on top of the other-lining up the ends. Don't worry about the strips being different widths. Fold the stacked ends in half length wise, use a generous seam allowance and sew across short end. When you tug them apart, the short ends will stay folded and the seam will flip to the inside of the fold. Now grab the opposite end of the bottom strip, and another strip. The bottom strip now goes on the top. Fold these two in half on the short end, and sew. I found it easier to sew these if I started with the fold going into the presser feet first....Keep at it and sew all the strips together in this manner. This actually goes pretty quickly-no need to backstitch or anything. Next, go back through the yarn and trim the ends of the threads and the extra seam allowance to about 1/4 inch.
Wind yarn into a skein-use a chair if you are swift-less like me. Make a few ties from scrap yarn to secure skein. Soak skein in cool water with some yarn wash. (Mine bled like crazy-maybe add some synthrapol if you have it...) Wring out, and twist tightly till the skein winds up onto itself. Let dry wound up to set lots of appealing wrinkles. (Just like washing and drying a broomstick skirt-again with the 90's!)